Slow earthquakes and afterslips prove that the Earth
does not have just two response time scales, i.e. that of
tectonic loading and that of regular earthquakes. A swarm
of slow earthquakes, with time constants of the order of
hundreds of seconds, has been detected by a laser
interferometer below the Gran Sasso massif (Italy). We
analyse and model these observations to identify a very
plausible source in a local fault, with no historic seismic
behavior. While slow earthquakes occurring in subduction
zones, and at the transition between locked and stably
sliding segments of the San Andreas fault, are often
associated with seismic events, in the case of the
Apennines there is no correlation between local seismicity
and slow earthquakes. Slow earthquakes, therefore, may
also represent a specific failure behavior for a seismically
locked fault, adding further complexity to the interpretation
of geologic data for seismic hazard estimates.